DE10332033A1 - Process for the preparation of metal powders or of metal hydride powders of the elements Ti, Zr, Hf, V, Nb, Ta and Cr - Google Patents

Abstract

A method for the production of metal powders or metal hydride powders of the elements Ti, Zr, Hf, V, Nb, Ta, and Cr is disclosed, whereby an oxide of the said elements is mixed with a reducing agent and said mixture, optionally with a hydrogen atmosphere (for the production fo metal hydrides), is heated until the reduction reaction commences, the reaction product is quenched, then washed and dried. The oxide used has an average particle size of 0.5 to 20 μm, a BET specific surface of 0.5 to 20 m2/g and a minimum content of 94 wt %.

Description

The The invention relates to a process for the production of metal powders, or of metal hydride powders of the elements Ti, Zr, Hf, V, Nb, Ta and Cr.

Metal powders of the elements Ti, Zr, Hf, V, Nb, Ta and Cr and powdered hydrides of these metals are used, for example, in the following fields of application: titanium in the production of titanium components for the aircraft and automotive industries, in the production of titanium alloys and in the manufacture sintered AlNiCo magnets; Titanium, zirconium and hafnium in the pyro-industry, in the manufacture of electric detonators (eg in airbags) and ignition delay elements, in getter materials in vacuum tubes, lamps, vacuum equipment and gas purification equipment; Hafnium as an alloying element in niobium, tantalum, titanium, molybdenum and tungsten alloys; Vanadium as an alternative electrode material in metal hydride / nickel hydride batteries and TiAl ₆ V ₄ alloys; Niobium in the manufacture of apparatus for the chemical industry and as an alloying element for ZrNb alloys (nuclear industry) and NbHfTi alloys (highly heat-resistant material for jet engines or blast chambers); Tantalum in capacitors.

Because of the sometimes very high demands on reliability the o.a. Products (e.g., airbag detonators), it is desirable the metal powder or metal hydride powder from batch to batch reproducible with consistent characteristics (in particular with regard to firing time, Ignition point, medium Grain size, particle size distribution and oxidation value).

The Production of the metal powder can be achieved by a reduction process respectively. For this purpose, oxides of the metals (Ti, Zr, Hf, V, Nb, Ta and Cr) e.g. reduced with calcium or calcium hydride. The reduction is carried out in a closed, inertizable and evacuated vessel. The or the reducing agents are usually added in excess. After Reduction, the resulting reducing agent oxides by lyes with acid and subsequent washing with water. The oxygen content The obtained metal powder is in this process between 1 and 5%.

alternative can the metal powder obtained from the respective metal by hydrogenation and dehydrogenation (HDH method). The respective metal is hydrogenated and can in this then brittle form to powder the desired Fineness be mechanically crushed. To damage by taking up To avoid oxygen and nitrogen must be high for hydrogenation pure hydrogen can be used. The comminution of the hydrogenated metal to the desired Grain size must also in a pure inert gas atmosphere (e.g., helium or argon) respectively. For subsequent removal of the hydrogen, the Metal hydride in a vacuum at elevated temperature Temperature decomposes. Likewise, the metal hydride powders are produced. Only the dehydration is dispensed with.

From Disadvantage of the metal powder and hydrides thus prepared is below other that this is not a reproducible burning time, no reproducible specific Surface, no reproducible particle size distribution and no reproducible ignition point exhibit.

task The invention is to overcome the disadvantages of the prior art and metal powder or metal hydride powder of the elements Ti, Zr, Hf, V, Nb, Ta and Cr provide a burning time of 4 s per 50 cm to 3000 s per 50 cm and an ignition point of 160 ° C to 400 ° C and in Individual cases beyond that exhibit.

The Burning time expressed in s / 50cm, it is determined as follows: The substance to be tested is first to eliminate disturbing Agglomerates over sieved two sieves with mesh sizes 250 μm and 45 μm. Possibly The sample can be moved carefully with a brush. to Determination of the burning time, the fines are used, which is the 45 μm sieve happened. 15 g of the sample are loosely placed on a subsequently described metal gutter given, with a cardboard card smoothed out and the surplus removed by stripping. The metal gutter is with two markings provided, which are a distance of 500 mm from each other. In addition to the initial marking is an about pea-sized amount of substance applied and ignited with a burner. With the help of a time recording Now the time is determined that the burning process to go through the distance between the beginning and the end marking needed. The analysis result the burning time is given in the dimension [s / 50 cm].

The ignition point is determined as follows: 10 g of the substance to be tested are introduced into a preheated, so-called "ignition block" and it is measured the temperature at which auto-ignition occurs. The firing block, consisting of an 70 mm long iron cube with a material and thermocouple hole (20 mm and 8 mm diameter, each bore 35 mm deep, 18 mm centers of bore), is inserted into the hole provided after inserting the thermometer or thermocouple with a blower on one just below the ignition Temperature lying preheated temperature. This point is determined by a pre-sample. A spatula tip (10 g) of the metal powder or hydride to be examined is then introduced into the material bore of the preheated ignition block and the block is heated with a full blower flame until the powder ignites spontaneously. The temperature reached is the ignition point.

Furthermore, it is desirable for the metal powder or metal hydride powder to have a content of at least 75% by weight of metal or metal hydride, preferably at least 88% by weight, particularly preferably at least 90% by weight, an average particle diameter of from 1 to 15 microns, a preferred particle size distribution d ₅₀ (measured by laser diffraction) of 1 to 20 microns and a BET specific surface area of 0.2 to 5 m ² / g.

Of the average grain diameter is measured using a "Fisher Sub-Sieve Size Grain Size Determiner" (hereinafter FSSS called) determined. A description of this method of measurement can be found in the "Instructions, Fisher Model 95 Sub-Sieve Sizer, Catalog No. 14-311, Part No. 14579 (Rev. C), published 01-94 "by Fisher Scientific. This measurement description is hereby incorporated by reference.

The object is achieved by a process for the production of metal powders or metal hydride powders of the elements Ti, Zr, Hf, V, Nb, Ta and Cr, in which an oxide of these elements mixed with a reducing agent and this mixture in a furnace optionally under a hydrogen atmosphere (then forming metal hydrides) is heated until the reduction reaction begins, the reaction product is leached and then washed and dried, wherein the oxide used has an average particle size of 0.5 to 20 .mu.m, preferably from 1 to 6 .mu.m, a specific surface area BET of 0.5 to 20 m ² / g, preferably from 1 to 12 m ² / g and particularly preferably from 1 to 8 m ² / g, and a minimum content of 94 wt .-%, preferably 96 wt .-% and particularly preferably 99% by weight.

The proportion of Fe and Al impurities in the oxide is preferably in each case <0.2% by weight, particularly preferably <0.1% by weight (calculated in each case as oxide). The proportion of Si impurities in the oxide is preferably <1.5% by weight, particularly preferably <0.3% by weight (calculated as SiO ₂ ). The proportion of Na impurities in the oxide is preferably <0.05% by weight (calculated as Na ₂ O). The proportion of P impurities in the oxide is preferably <0.2 wt .-% (calculated as P ₂ O ₅ ). The loss on ignition of the oxide at 1000 ° C. (weight constancy) is preferably <1% by weight, more preferably <0.5% by weight. The tamped density according to EN ISO 787-11 (formerly DIN 53194) of the oxide is preferably 800 to 1600 kg / m ³ . The oxide may be replaced by additions of MgO, CaO, Y ₂ O ₃ or CeO ₂ up to a proportion of 15% by weight.

It has been found that, in the targeted selection of the oxidic raw materials with the described properties and subsequent performance of the process, products are obtained which have a firing time of 4 s per 50 cm to 3000 s per 50 cm, an ignition energy of 1 μJ to 1 mJ, a mean particle size of 1 to 8 microns, a BET specific surface area of 0.2 to 5 m ² / g, an ignition point of 160 ° C to 400 ° C and in individual cases beyond, in each case reproducible particle size distributions are obtained. The combination of average grain size and specific surface area in the respective specified ranges of the oxide starting compound leads, together with the specified minimum content to the desired product.

When Reducing agents can are preferably used: alkaline earth metals and alkali metals and their respective hydrides. Particularly preferred are magnesium, calcium, Calcium hydride and barium or defined mixtures thereof. Prefers the reducing agent has a minimum content of 99% by weight, especially preferably 99.5 wt .-%.

ever after the hydrogen addition amount during the reduction process in the oven become powdery pure metals, partially hydrogenated metals or metal hydrides obtained. The higher the hydrogen content of the process product is the greater the burning time (i.e., the metal burns slower) and the higher the ignition point and vice versa.

The Leaching of the reaction product is preferably concentrated hydrochloric acid made, more preferably in slight excess is used.

The The invention is explained in more detail below with reference to examples.

Example 1: Preparation of zirconium powder

43 kg ZrO ₂ (powdered zirconium oxide (natural baddeleyite) having the following properties: ZrO ₂ + HfO ₂ min 99.0%, HfO ₂ 1.0-2.0%, SiO ₂ 0.5% max, TiO ₂ max 0.3%, Fe ₂ O ₃ 0.1% maximum, ignition loss 0.5% max, mean particle size (according to FSSS) 4 - 6 μm, proportion of monoclinic crystal structure at least 96%, specific surface area (according to BET) 0.5-1.5 m ² / g) and
31.5 kg Ca (calcium in the form of granules with the following properties: Ca min 99.3%, Mg max 0.7%)
were ge 20 minutes under argon atmosphere ge mixed. Then the mixture was added to a container. The container was placed in an oven, which was subsequently sealed and filled with argon to an overpressure of 100 hPa. The reaction furnace was heated in one hour to a temperature of about 1250 ° C. As soon as the reaction mass reached the temperature of the furnace, the reduction reaction started: ZrO ₂ + 2 Ca → Zr + 2 CaO

60 minutes after switching on the heater, it was switched off again. After the temperature had fallen to <50 C °, the reaction mass was removed from the crucible and leached with concentrated hydrochloric acid. A zirconium powder was obtained with the following analysis: Zr + Hf 96.1%; Hf 2.2%; O 0.7%; Si 0.21%; H 0.16%; Mg 0.11%; Ca 0.13%; Fe 0.07%; Al 0.1%; Cl 0.002%; average grain size 4.9 μm; Particle size distribution d ₅₀ 9.9 μm; specific surface area 0.5 m ² / g; Ignition point 220 ° C; Burning time 80 sec / 50 cm.

Example 2: Preparation of zirconium powder

36 kg ZrO ₂ (pulverulent zirconium oxide having the following properties: ZrO ₂ + HfO ₂ min 99.0%, HfO ₂ 1.0-2.0%, SiO ₂ 0.2% max, TiO ₂ 0.25 max % Fe ₂ O ₃ max 0.02%, ignition loss 0.4% max, mean grain size (FSSS) 3 - 5 μm, monoclinic crystal structure min 96%, BET specific surface area 3.0 - 4.0 m ² / g) and
17 kg Mg (magnesium in the form of granules having the following properties: Mg at least 99.8%, bulk density max 0.4 - 0.5 g / cm ³
were used as in Example 1 in a container in the oven. The oven was heated to 1050 ° C. As soon as the reaction mass reached the temperature of the furnace, the reduction reaction started: ZrO ₂ + 2 Mg → Zr + 2 MgO

The heater was switched off 20 minutes after the start of the reduction. After the temperature had fallen to <50 °, the reaction mass was removed from the crucible and leached with concentrated hydrochloric acid. A zirconium powder was obtained with the following analysis: Zr + Hf 91.7%; O 1.6%; Si 0.14%; H 0.13%; Mg 0.59%; Ca <0.001%; Fe 0.045%; average particle size 2.5 μm; Particle size distribution d ₅₀ 4.3 μm; Ignition point 175 ° C; Burning time 24 sec / 50 cm.

Claims (21)

Process for the preparation of metal powders or metal hydride powders of the elements Ti, Zr, Hf, V, Nb, Ta and Cr, in which an oxide of these elements is mixed with a reducing agent and this mixture is optionally heated in a furnace under hydrogen atmosphere (then metal hydrides are formed) is heated until the reduction reaction begins, the reaction product is leached and then washed and dried, characterized in that the oxide used has an average grain size of 0.5 to 20 microns, a BET specific surface area of 0.5 to 20 m ² / g and has a minimum content of 94 wt .-%. Method according to claim 2, characterized in that the mixture is heated in the oven to 800 to 1400 ° C. Method according to claim 1 or 2, characterized the oxide used has an average grain size of 1 up to 6 μm having. Method according to one of claims 1 to 3, characterized in that the oxide used has a BET specific surface area of 1 to 12 m ² / g. A method according to claim 4, characterized in that the oxide used has a BET specific surface area of 1 to 8 m ² / g. Method according to one of claims 1 to 5, characterized that the oxide used has a minimum content of 96 wt .-%. Method according to Claim 6, characterized that the oxide used has a minimum content of 99 wt .-%. Method according to one of claims 1 to 7, characterized that the proportion of Fe and Al impurities in the oxide in each case <0.2 wt .-% (calculated as oxide). Method according to claim 8, characterized in that that the proportion of Fe and Al impurities in the oxide in each case <0.1 wt .-% (calculated as oxide) is. Method according to one of claims 1 to 9, characterized in that the proportion of Si impurities in the oxide <1.5 wt .-% (calculated as SiO ₂ ). A method according to claim 10, characterized in that the proportion of Si impurities in the oxide <0.3 wt .-% (calculated as SiO ₂ ). Method according to one of claims 1 to 11, characterized in that the proportion of Na impurities in the oxide <0.05 wt .-% (calculated as Na ₂ O). Method according to one of claims 1 to 12, characterized in that the proportion of P-impurities in the oxide <0.2 wt .-% (equ net as P ₂ O ₅ ). Method according to one of claims 1 to 13, characterized that the loss of ignition of the Oxides at 1000 ° C (Constant weight) <1% by weight is. Method according to one of claims 1 to 14, characterized in that the tamped density according to EN ISO 787-11 (formerly DIN 53194) of the oxide is 800 to 1600 kg / m ³ . Method according to one of claims 1 to 15, characterized in that the oxide is replaced up to a proportion of 15 wt .-% by additions of MgO, CaO, Y ₂ O ₃ or CeO ₂ . Method according to one of claims 1 to 15, characterized that as the reducing agent alkaline earth metals and / or alkali metals and / or their hydrides are used. A method according to claim 17, characterized in that are used as reducing agent Mg, Ca, CaH ₂ , or Ba. Method according to one of claims 1 to 18, characterized the reducing agent has a minimum content of 99% by weight. Method according to one of claims 1 to 19, characterized the reaction is carried out under protective gas. Method according to one of claims 1 to 20, characterized that the leaching of the reaction product is carried out with hydrochloric acid.